Air screw-propeller.



R. KORNMANN. AIR SCREW PRQPELL'BB.. APPLICATION FILED JULY 15, 1912.

m/lTESEES COLUMBIA PLANOGRAPH C0.. WASHINGTON. DA c.

RALF KORNMANN, OF BERLIN, GERMANY.

AIR SCREW -PROPELLER.

Specification of Letters Patent.

Patented Apr. 21, 1914.

Application filed July 15, 1912. Serial No. 709,369.

To all whom. it may concern Be it known that I, RALF KonNMANiv, engineer, a citizen of the Swiss Republic, residing at G Tauentzienstrasse, BerlinGrermany, have invented certain new and useful Improvements in Air Screw-Propellers; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

My present invention relates to air-screwpropellers, more especially to propellers of this description made of wood.

The object of my invention is to provide a propeller which shall be lighter and stronger and shall moreover produce a stronger driving force for a given motor power than propellers as hitherto constructed. To achieve this end I give the vanes of a propeller a certain curvature disposed in such a manner that the direction of the resultant of the forces produced by the action of the pro peller coincides with the direction of the grain of the wood of which the propeller is constructed and also with the direction of the seams uniting the different parts of the structure.

rlwo forces mainly have to be considered, firstly the reaction of the air pressure produced by the propeller, which force acts in a direction parallel to the propeller shaft and forward with relation to the direction of travel of the vehicle that is propelled, and secondly the centrifugal force which acts in a radial and outward direction. Both hese forces increase as the number of revolutions performed by the propeller in the unit of time increases and therefore the direction of the resultant force in every part of the vanes is practically constant for all speeds, but increasingly inclined forward for parts situated on increasing diameters. To comply with these conditions I give the vanes of my propeller a curvature with relation to a plane normal to the propeller shaft and such that they present their convex side rearward with relation to the direction of propulsion, increasing the forward inclination with increasing` diameter.

To construct a propeller of this kind I proceed as follows: A number of thin boards or strips of wood are cut out having a width somewhat larger than that of the vanes I desire to produce, and of such thickness that they can, without overstraining, be

bent to the curvature the propeller is intended to receive. I then place the boards or strips thus prepared on one another and ,clamp them together with a rigid gage block, or two such blocks, having the desired curvature' and in this position unite them by means of glue or any other suitable cement. When the binding substance has hardened, the clamping pressure can be withdrawn and it is found that the composite block of wood thus produced, does not return into its original straight shape, bei cause the expansion and compression, given to adjacent surfaces of the single boards by bending, is retained by the binding substance uniting them, thus also retaining the curvature corresponding to these expansions and compressions. The vanes are then carved out of the block thus prepared in the usual manner.

The drawing is a sectional elevation of a propeller constructed according to my invention.

The line A B indicates the axis of the propeller shaft and the broken curved lines c, c represent the surfaces of the boards or strips composing a curved block C from which the propeller is carved out. The arrow indicates the direction in which the vehicle is to be propelled, the curvature of the propeller being so disposed that the convex side faces the body of air which is cornpressed by the action of the propeller. The force resulting from the air pressure and the centrifugal action will approximately coincide with the direction of the grain of the wood and with the seams c uniting the single boards.

I have ascertained by experiment that, by thus favorably disposing the stresses due to the propellers action, I can considerably reduce the cross section of the vanes as compared with propellers as hitherto constructed and thereby produce a proportional increase of efficiency.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is 1. A propeller having blades curved to present their convex side` rearward with relation to the direction of propulsion, said blades composed of a plurality of united curved thin wooden sections, the curvature of said sections corresponding to the curvature of the propeller.

2. A propeller comprising a plurality of unitarily united curved sections so bent as to present their convex side rearward with relation to the direction of propulsion.

3. A propeller having` a plurality of blades bent to a curvature substantially corresponding to the resultant of the force produced by the Wind pressure and by the centrifugal force of the propeller.

4L. A propeller having a plurality of blades bent to a curvature substantially corresponding to the resultant of the force pro- Copies of this patent may be obtained for duced by the Wind pressure and by theccntrifugal force of thepropeller, said blades composed of a plurality of united curved thin Wooden sectens, the curvature of which corresponds to, the curvature of the propeller.

.In testilnonyiwhereof I have affixed my signature, in presence of two Witnesses.

t RALF KORNMANN. VVitnessesg HENRY HASPER, QLDMIAR HAUPT.

flve cents each, bg addressing the Commissioner of Patents, Washington, IL Q. 

